1. Field of the Invention
The present invention relates to devices that enable the directional swivelling or orienting of a detector head of a gamma camera, preferably a tomographic gamma camera, appropriately in relation to the patient undergoing an examination with this gamma camera.
2. Description of the Prior Art
Gamma cameras are described, for example, in the U.S. Pat. No. 3,011,057 by Anger. A gamma camera is an apparatus comprising a rotating stand, which is fixed or movable with respect to the ground and carries a detector, also called a detector head, at the end of the arm. This detector is provided with an array of photomultiplier tubes, the input faces of which are juxtaposed with one another and constitute the detection surface of the detector head and its detection field.
The following is the principle of the examination. A radioactive substance is injected into a patient to be examined. This substance is thallium for example. The radioactive emission excites a scintillator crystal of the detector which converts the energy of the gamma photons into a light energy that can be detected by the photomultiplier tubes. The scintillator crystal is preceded, in a standard way, by a collimator defining a sighting direction and characterized by a focal point. This focal point is pushed back to infinity in the case of collimators with parallel, straight or inclined holes. The focal point is at a finite distance, which is positive or negative, in the case of convergent or divergent collimators. The focus is off-centered with respect to a central sighting direction.
The scintillations emitted are detected by the photomultiplier tubes which produce electrical signals depending on the light intensity received. By carrying out barycentric tracking operations on all these electrical signals, it is possible, in a known way, to determine the localization X Y of the origin of the scintillation in the detection field. An incremental acquisition is then carried out by totalizing the number of scintillations (or strokes) detected per localization element called a pixel.
By leaving the detector head in a given position for a certain time above the examined body, it is then possible, for a given angle of sight, called a projection, to obtain an image that reveals the concentration of the emitting substance in the body. The tomographic examination consists in acquiring one image per angle of sight, for a large number of angles of sight, evenly spaced out on an angular sector of at least 180.degree.. It is then possible, with computation algorithms, notably filtered back projection, to reconstitute the image of a volume of the body.
The patient being examined is stretched out on a bed. The bed can be moved directionally with respect to a supporting frame that is fixed, or movable in translation, which supports the gamma camera by means of hinged elements. By combining these different means, it is thus possible to swivel the gamma camera directionally with respect to the patient's body to obtain the desired image of the organ. For obvious reasons of cost, it is necessary to limit, as far as possible, the number of hinges of the elements that support the gamma camera, within the limits of the results to be obtained.
Until recently, the sensitive part of the gamma camera was round. This meant that, all things being equal, the orientation of the patient around the normal to this sensitive part was irrelevant. The instrument used now is a gamma camera with a detector head that has no symmetry of revolution. Its shape may be rectangular, with corners that may or may not be truncated or that may even be elliptical. It is characterized by a big axis and a small axis, which are axes of symmetry in the plane of the detector. The dimension of the big axis is greater than that of the small axis. In these cases, the orientation of the patient about this normal is no longer irrelevant to the most efficient use of the detection field. This requirement further complicates the hinges that have to be provided for.
For the most efficient orientation of the field of detection of the gamma camera, the invention proposes a pin for the directional swivelling of the detector head. This directional swivelling pin is perpendicular to the field of detection of this head. It enables the small axis of this head to be oriented along the axis of the patient, whether the patient is placed in the rotation axis of the stand of the gamma camera or perpendicularly to this rotation axis of the stand.